260
H. Michaelis and w.J. Wolff
The habitat division on the Banc d' Arguin is based on a map presented by
Altenburg et al. (1982). It was actualized in a few details by the observations of
September 1988. For the Juist area, a series of aerial photographs (black and
white-infrared, 1:15,000) from a low-tide situation in June 1988 was analyzed.
In combination with ground truth, all discernable structures were used for
characterization and mapping of physiographical units.
12.3 Results
12.3.1 Habitat Division .
On the tidal flats of the Banc d' Arguin, habitats had already been distinguished by earlier surveys (Altenburg et al. 1982; Wolff et al. 1993a):
- Stands of seagrasses with the dominant species Zostera noltii covering
about 80 % of the area. Muddy and mixed sediments prevail (Michaelis
1993). Within the Zostera stands, minor areas covered by the trichomic alga
Vaucheria occur.
- Light sandy flats cover about 20 % of the intertidal areas. Michaelis (1993)
and Wolff et al. (1993a) give data on grain-size distributions and related
sediment parameters.
Additional habitats of low quantitative relevance, and therefore not indicated in Fig. 12.2, are exposed beaches and a scant mangrove of Avicennia
africana. Finally, the sebkha, a supralittoral transition area between the tidal
flats and the desert, covers extensive beach plain areas with irregular inundation (Fig. 12.2).
In the Juist area, ten different habitats could be distinguished. The grainsize distribution of the sediments ranges from fine sand to fine-sandy
medium sand (Obert and Michaelis, in prep.). The habitats are arranged on a
gradient from the wave-exposed seaside to the sheltered positions towards the
mainland and behind the island ofJuist (Fig. 12.3). The main habitats are light
sandy flats forming fringes at the edge of the more exposed sand banks and
dark sandy flats covering almost three-quarters of the whole area in the more
sheltered positions. The habitat "high sands" are bare sand banks that project
to a small degree above the mean high-water level and are irregularly inundated (Reineck 1956).
H. Michaelis and w.J. Wolff
The habitat division on the Banc d' Arguin is based on a map presented by
Altenburg et al. (1982). It was actualized in a few details by the observations of
September 1988. For the Juist area, a series of aerial photographs (black and
white-infrared, 1:15,000) from a low-tide situation in June 1988 was analyzed.
In combination with ground truth, all discernable structures were used for
characterization and mapping of physiographical units.
12.3 Results
12.3.1 Habitat Division .
On the tidal flats of the Banc d' Arguin, habitats had already been distinguished by earlier surveys (Altenburg et al. 1982; Wolff et al. 1993a):
- Stands of seagrasses with the dominant species Zostera noltii covering
about 80 % of the area. Muddy and mixed sediments prevail (Michaelis
1993). Within the Zostera stands, minor areas covered by the trichomic alga
Vaucheria occur.
- Light sandy flats cover about 20 % of the intertidal areas. Michaelis (1993)
and Wolff et al. (1993a) give data on grain-size distributions and related
sediment parameters.
Additional habitats of low quantitative relevance, and therefore not indicated in Fig. 12.2, are exposed beaches and a scant mangrove of Avicennia
africana. Finally, the sebkha, a supralittoral transition area between the tidal
flats and the desert, covers extensive beach plain areas with irregular inundation (Fig. 12.2).
In the Juist area, ten different habitats could be distinguished. The grainsize distribution of the sediments ranges from fine sand to fine-sandy
medium sand (Obert and Michaelis, in prep.). The habitats are arranged on a
gradient from the wave-exposed seaside to the sheltered positions towards the
mainland and behind the island ofJuist (Fig. 12.3). The main habitats are light
sandy flats forming fringes at the edge of the more exposed sand banks and
dark sandy flats covering almost three-quarters of the whole area in the more
sheltered positions. The habitat "high sands" are bare sand banks that project
to a small degree above the mean high-water level and are irregularly inundated (Reineck 1956).